One of a pair of small (wing length 4.5 to 6.5 mm), slim, long-legged Bibio species, the other being Bibio clavipes. In both species, the legs are much slimmer than most other Bibio species (except venosus which is much larger, flies in spring and has dark wing veins). The males of B. longipes are all black, the females have a black body but reddish legs, and usually have clearer wings. B. longipes has a dark wing stigma which is well formed and extends into the costal cell, and the palps are shorter than those of B. clavipes. 

The other similar species, Bibio clavipes, has a paler stigma that does not extend into the tip of the costal cell, longer palps and females that are extensively reddish.

Unless identified by a recognised expert, a photo is required and the specimen should be examined with a microscope. In the comments box, state the key or ID method used and describe the size and identifying characters.

It can be quite common in in ancient broadleaved woodland with males often swarming along woodland rides. Females seem to be much more elusive than males.

Flies in September and October.

The larvae are presumed to develop in woodland and grassland soils.

Widely recorded in Britain but is localised and probably under-recorded due to its late flight period. 

Status in Leicestershire and Rutland not known.